Examples of systems of this type are shown in U.S. Pat. Nos. 4,699,163 and 5,720,309 (issued Feb. 24, 1998) both of the present inventor which includes an elongate pipe section having a rear end for connection to the hose and a forward end connected to a cylindrical housing. At a rear face of the housing is provided a plurality of rearwardly extending jets surrounding the pipe section. A plurality of skid bars are attached to the housing longitudinally of the housing at angularly spaced positions around the housing with those skid bars extending from the rear face of the housing rearwardly and inwardly for attachment to the pipe section.
Further examples are shown in U.S. Pat. No. 3,380,461 (Maasberg), U.S. Pat. No. 3,678,948 (Hedges assigned to Rockwell Manufacturing Co.); U.S. Pat. No. 3,814,330 (Masters assigned to McNeil Corporation) and U.S. Pat. No. 4,073,302 (Jones).
Masters shows a nozzle having four lobes each lying in a substantially axial plane with the lobes arranged at right angles and each lobe carries two jet nozzles. This arrangement is disadvantageous in that the nozzles are carried on the lobes and therefore can be engaged into the material at the base of the pipe thus reducing flow.
Maasberg discloses a head which is generally a flat body with nozzles at the front face. Again the nozzles can engage into the material reducing flow.
Hedges discloses a relatively complex arrangement with two heads carried on a central fin section with the fins welded to a connecting pipe section at spaced positions around the axis of the pipe section. This arrangement is relatively complex and bulky so that the cost of manufacture is increased and the proper flow of material and flushing water may not be achieved.
Jones discloses an arrangement with skids which run on the inside surface of the pipe with a simple nozzle and is therefore carried centrally of the pipe. This arrangement is impractical in view of the difficulty of running along the length of the pipe which can have obstructions, bends and the like.